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Homework Help: Floating bed problem

  1. Aug 20, 2009 #1
    1. The problem statement, all variables and given/known data
    There is a large bed floating in sea with the density of 765 kg/m^3. What fraction of the bed's volume will be under the surface of the water? The density of sea water is 1035 kg/m^3.

    2. Relevant equations
    Fb = Density * v * gravity

    3. The attempt at a solution
    I know its a buoyancy problem, but i have no idea where to get started. i can't find the Fb b/c volume's not given. maybe i have to set them equal to each other?
    765 kg/m^3 * Volume * gravity = 1035 kg/m^3 * V * g
    so it woulbd be .739% of the volume.
    It seems too easy or is this right?
    Thank you!
  2. jcsd
  3. Aug 20, 2009 #2


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    Science Advisor
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    Gold Member

    Call the fraction of the volume that is under water f.

    Then the buoyant force is

    [tex]BF = \rho_{water}f V g[/tex]

    where V is the entire volume of the bed. Then the weight of the bed in terms of its density and volume is ...

    so for the bed to float ...
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